The beam loading effect is a considerable issue for a high average current beam. We apply a novel method without utilizing the specious beam current value to rigorously analyze the beam loading effect in S-band linacs...The beam loading effect is a considerable issue for a high average current beam. We apply a novel method without utilizing the specious beam current value to rigorously analyze the beam loading effect in S-band linacs. By tracking every macro-particle＇s state and using the energy conservation law, power dissipated from the beam is calculated in each cell. In the new particle-based algorithm, the concept of equivalent beam current is proposed. Its value is not constant and it has a small variation through the accelerating structure. Also, we introduce the iteration algorithm as comparison and we find that the two algorithms coincide with each other very well.展开更多
To meet the requirements of high performance THz-FEL （Free Electron Laser）, a compact scheme of FEL injector was proposed. A thermionic cathode was chosen to emit electrons instead of a photo-cathode with its comple...To meet the requirements of high performance THz-FEL （Free Electron Laser）, a compact scheme of FEL injector was proposed. A thermionic cathode was chosen to emit electrons instead of a photo-cathode with its complex structure and high cost. The effective bunch charge was improved to ~200 pC by adopting an enhanced EC-ITC （External Cathode Independently Tunable Cells） RF gun to extract micro-bunches; back bombardment effects were almost eliminated as well. Constant gradient accelerator structures were designed to improve energy to ~14 MeV, while the focusing system was applied for emittance suppressing and bunch state maintenance. The physical design and beam dynamics of the key components for the FEL injector were analyzed. Furthermore, start- to-end simulations with multi-pulses were performed using homemade MATLAB and Parmela. The results show that continual high brightness electron bunches with a low energy spread and emittance could be obtained stably.展开更多
The beam tail effect of multi-bunches will influence the electron beam performance in a high intensity thermionic RF gun. Beam dynamic calculations that illustrate the working states of single beam tail and multi-puls...The beam tail effect of multi-bunches will influence the electron beam performance in a high intensity thermionic RF gun. Beam dynamic calculations that illustrate the working states of single beam tail and multi-pulse feed-in of a performance-enhanced EC-ITC （external cathode independent tunable cavity） RF gun for an FEL （free electron laser） injector are performed to estimate the extracted bunch properties. By using both Parmela and homemade MATLAB codes, the effects of a single beam tail as well as interactions of multi-pulses are analyzed, where a ring-based electron algorithm is adopted to calculated RF fields and the space-charge field. Furthermore, the procedure of unexpected deviated-energy particles mixed with an effective bunch head is described by the MATLAB code as well. As a result, the performance-enhanced EC-ITC RF gun is proved to have the capability to extract continual stable bunches suitable for a high requirement THz-FEL.展开更多
An EC-ITC （External-Cathode Independently Tunable Cells） RF gun was employed with the aim of obtaining short-pulse bunches with high peak current for a terahertz radiation source. A gridded DC gun plays a key role a...An EC-ITC （External-Cathode Independently Tunable Cells） RF gun was employed with the aim of obtaining short-pulse bunches with high peak current for a terahertz radiation source. A gridded DC gun plays a key role as the external injecting electron source of the ITC RF gun, the performance of which determines the beam quality in the injector and transport line. In order to make the beam well compressed in the ITC RF gun, the energy of the electrons acquired from the gridded DC gun should be 15 keV at most. A proper structure of the gridded gun with double-anode is shown to overcome the strong space- charge force on the cathode, which is able to generate 6 μs beam with 4.5 A current successfully.展开更多
Terahertz radiation has broad application prospects due to its ability to penetrate deep into many organic materials without the damage caused by ionizing radiations. A free electron laser （FEL）-based THz source is ...Terahertz radiation has broad application prospects due to its ability to penetrate deep into many organic materials without the damage caused by ionizing radiations. A free electron laser （FEL）-based THz source is the best choice to produce high-power radiation. In this paper, a 14 MeV injector is introduced for generating high-quality beam for FEL, is composed of an EC-ITC RF gun, compensating coils and a travelling-wave structure. Beam dynamics simulations have been done with ASTRA code to verify the design and to optimize parameters. Simulations of the operating mode at 6 MeV have also been executed.展开更多
Since the beta function of the electron beam within the undulator has a great influence on the power gain of the free electron laser（FEL）,optimization of the undulator lattice becomes important.In this paper,the tra...Since the beta function of the electron beam within the undulator has a great influence on the power gain of the free electron laser（FEL）,optimization of the undulator lattice becomes important.In this paper,the transfer matrix of the planar undulator is obtained from differential equations of the electron motion.Based on this,the lattice function of the planar undulator in a terahertz FEL oscillator proposed by Huazhong University of Science and Technology（HUST-FEL） is optimized and the expressions of the average beta function are derived.The accuracy of the optimization result was confirmed well by the numerical method.The application range of this analytical method is given as well.At last,the emittance growth in the horizontal direction due to the attenuation of the magnetic field is discussed.展开更多
文摘The beam loading effect is a considerable issue for a high average current beam. We apply a novel method without utilizing the specious beam current value to rigorously analyze the beam loading effect in S-band linacs. By tracking every macro-particle＇s state and using the energy conservation law, power dissipated from the beam is calculated in each cell. In the new particle-based algorithm, the concept of equivalent beam current is proposed. Its value is not constant and it has a small variation through the accelerating structure. Also, we introduce the iteration algorithm as comparison and we find that the two algorithms coincide with each other very well.
文摘To meet the requirements of high performance THz-FEL （Free Electron Laser）, a compact scheme of FEL injector was proposed. A thermionic cathode was chosen to emit electrons instead of a photo-cathode with its complex structure and high cost. The effective bunch charge was improved to ~200 pC by adopting an enhanced EC-ITC （External Cathode Independently Tunable Cells） RF gun to extract micro-bunches; back bombardment effects were almost eliminated as well. Constant gradient accelerator structures were designed to improve energy to ~14 MeV, while the focusing system was applied for emittance suppressing and bunch state maintenance. The physical design and beam dynamics of the key components for the FEL injector were analyzed. Furthermore, start- to-end simulations with multi-pulses were performed using homemade MATLAB and Parmela. The results show that continual high brightness electron bunches with a low energy spread and emittance could be obtained stably.
文摘The beam tail effect of multi-bunches will influence the electron beam performance in a high intensity thermionic RF gun. Beam dynamic calculations that illustrate the working states of single beam tail and multi-pulse feed-in of a performance-enhanced EC-ITC （external cathode independent tunable cavity） RF gun for an FEL （free electron laser） injector are performed to estimate the extracted bunch properties. By using both Parmela and homemade MATLAB codes, the effects of a single beam tail as well as interactions of multi-pulses are analyzed, where a ring-based electron algorithm is adopted to calculated RF fields and the space-charge field. Furthermore, the procedure of unexpected deviated-energy particles mixed with an effective bunch head is described by the MATLAB code as well. As a result, the performance-enhanced EC-ITC RF gun is proved to have the capability to extract continual stable bunches suitable for a high requirement THz-FEL.
基金Supported by National Natural Science Foundation of China(10875116)
文摘An EC-ITC （External-Cathode Independently Tunable Cells） RF gun was employed with the aim of obtaining short-pulse bunches with high peak current for a terahertz radiation source. A gridded DC gun plays a key role as the external injecting electron source of the ITC RF gun, the performance of which determines the beam quality in the injector and transport line. In order to make the beam well compressed in the ITC RF gun, the energy of the electrons acquired from the gridded DC gun should be 15 keV at most. A proper structure of the gridded gun with double-anode is shown to overcome the strong space- charge force on the cathode, which is able to generate 6 μs beam with 4.5 A current successfully.
文摘Terahertz radiation has broad application prospects due to its ability to penetrate deep into many organic materials without the damage caused by ionizing radiations. A free electron laser （FEL）-based THz source is the best choice to produce high-power radiation. In this paper, a 14 MeV injector is introduced for generating high-quality beam for FEL, is composed of an EC-ITC RF gun, compensating coils and a travelling-wave structure. Beam dynamics simulations have been done with ASTRA code to verify the design and to optimize parameters. Simulations of the operating mode at 6 MeV have also been executed.
文摘Since the beta function of the electron beam within the undulator has a great influence on the power gain of the free electron laser（FEL）,optimization of the undulator lattice becomes important.In this paper,the transfer matrix of the planar undulator is obtained from differential equations of the electron motion.Based on this,the lattice function of the planar undulator in a terahertz FEL oscillator proposed by Huazhong University of Science and Technology（HUST-FEL） is optimized and the expressions of the average beta function are derived.The accuracy of the optimization result was confirmed well by the numerical method.The application range of this analytical method is given as well.At last,the emittance growth in the horizontal direction due to the attenuation of the magnetic field is discussed.
